A widely used and successful commercial process for synthesizing acetic acid involves the catalyzed carbonylation of methanol with carbon monoxide. The catalysis contains rhodium and/or iridium and a halogen promoter, typically methyl iodide. The reaction is conducted by continuously bubbling carbon monoxide through a liquid reaction medium in which the catalyst is dissolved. The reaction medium also comprises methyl acetate, water, methyl iodide and the catalyst. Conventional commercial processes for carbonylation of methanol include those described in U.S. Pat. Nos. 3,769,329, 5,001,259, 5,026,908, and 5,144,068, the entire contents and disclosures of which are hereby incorporated by reference. Another conventional methanol carbonylation process includes the Cativa™ process, which is discussed in Jones, J. H. (2002), “The Cativa™ Process for the Manufacture of Acetic Acid,” Platinum Metals Review, 44 (3): 94-105, the entire content and disclosure of which is hereby incorporated by reference.
In the production of acetic acid there may be several limits on the capacity of the system. One such limit is the removal of heat from the reaction. Methanol carbonylation is an exothermic reaction and regulating the heat is necessary for maintaining efficient production rates. Conventional systems use a flasher to remove about half of the heat of the reaction. U.S. Pat. No. 5,364,963 also describes a cooling a portion of the carbonylation product with an indirect hear exchange. As production increase the heat that needs to be remove also increases. Removing the increase in heat with the flasher may be less efficient, and may reduce the overall production of acetic acid.
The heat of the reaction may also be recovered. U.S. Pat. No. 6,175,039 discloses removing the heat of reaction from the highly exothermic process by using a steam boiler heated by the pump-around stream. The heat from the reaction may also be transferred to other systems. U.S. Pat. No. 6,114,576 discloses a process for the production of carboxylic acid in the presence of solid catalyst particles that uses the exothermic heat of reaction with high efficiency in recovering the carboxylic acid product. This process uses indirect heat exchange to transfer the heat of reaction to another stream, without the need for an additional heat transfer fluid such as steam. U.S. Pat. No. 7,465,823 discloses a process and system in which a portion of the heat produced during the production of the acetic acid is transferred to a vinyl acetate production and/or purification process and system to facilitate production and/or purification of a vinyl acetate product.
Increasing production rates may also place capacity limitations on the purification systems. Expanding capacity in commercial purification systems requires increasing the size of the distillation columns. Larger distillation columns also may require reconfiguration of the column, piping, foundations, and utilities to expand capacity. The associated downtime to increase capacity make these changeovers to larger-capacity distillation columns economically unattractive.
As will be appreciated by one of skill in the art, there is always incentive for improvement to existing processes for the production of acetic acid. The present invention provides some such improvements.